Caroline Arcini of Sweden’s National Heritage Board analysed 557 skeletons from four major Viking-age Swedish cemeteries and discovered that around 10 per cent of men, but none of the women, bore horizontal grooves across the upper front teeth.

The marks, which were cut deep into the enamel, are often found in pairs or triplets and appear precisely made. They might have marked certain men as members of a group of tradesmen or warriors, or signified their ability to withstand pain, says Arcini…

*snip*

Most of the men bearing the grooves were young, but in the absence of any distinctive injuries or artefacts buried with the skeletons, the exact reason for the marks remains a mystery.

This is the first known case of tooth filing in Europe, but it was common practice in the Americas between AD 800 and 1050. Since the skeletons date from around the same time, this raises the possibility that the Vikings picked up the practice during their travels. Arcini hopes future finds will reveal where the practice arose and how it spread.

The above is a human tooth. If you look closely you can see faint grooves running horizontally across it’s surface. These grooves are called perikymata and represent growth. More specifically they represent growth cycles of about 6-14 days. Below is a high magnification detail from a thin section.

High magnification detail from the same thin section showing the regular growth structures found in enamel (polarised transmitted light microscopy). The approximately weekly growth layers, known as brown striae of Retzius, can be seen running from bottom left to top right. The enamel prisms run across from left to right, along which cross-striations can be seen (arrows). The cross-striations represent circadian (i.e. daily) growth markers and can be used to determine the precise timing of crown formation, as well as the timing of any disruption to this formation.

In theory one could count the number of perikymata on a tooth multiply it by 6-12 days and come up with an estimate of how long it took the tooth to form – getting at the same time an estimate of the length of childhood. Such studies have a long history in anthropology and recently this idea was applied to Neanderthal teeth. At issue is how long Neanderthals took to reach maturity – if they took less time than anatomically modern humans then that would obviously have bearing on the whole “Out of Africa/Multiregional Continuity” debate. Recently a team of researchers performed a study on the perikymata of Neanderthal teeth:

For the study, the researchers used precise dental impressions Guatelli-Steinberg and Larsen made of 55 teeth believed to come from 30 Neanderthal individuals. These were compared to 65 teeth from 17 Inuit, 134 teeth from 114 southern Africans and 115 teeth from as many Newcastle residents. In all cases, the researchers tallied the number of perikymata on the enamel surface of the teeth.

Guatelli-Steinberg said that the results showed that the enamel formation times for the Neanderthals fell easily within the range of time shown by teeth from the three modern populations – a conclusion that did not support a shorter childhood for the Neanderthals.

Enticing though it may be, these new findings haven’t convinced the researchers that a Neanderthal childhood was equal to a modern human’s.

“The missing key bit of data to show that would be evidence for when the first molar tooth erupted in the Neanderthals, and we simple have no evidence of when that occurred,” she said.

The length of time is important, the researchers say, because unlike all other primates, humans have an extended period of childhood growth, during which brain matures both in size and through experiences. Some earlier hominids matured far more quickly than modern humans.

“The question is when exactly did that pattern of development evolve in the growth of humans,” she said.

The new technique, developed by researchers at Lawrence Livermore National Laboratory (LLNL) and the Karolinska Institute in Sweden, determines the amount of carbon-14 in tooth enamel. Scientists can relate the extensive atmospheric record for carbon-14 to when the tooth was formed and calculate the age of the tooth, and its owner, to an accuracy of within about 1.6 years.

“Unlike most other tissue, dental enamel doesn’t turn over,” said Bruce Buchholz of LLNL’s Center for Accelerator Mass Spectrometry, where the enamel samples were analyzed. “Whatever carbon gets laid down in enamel during tooth formation stays there, so tooth enamel is a very good chronometer of the time of formation.

“We were surprised at how well it worked,” he said. “And if you look at multiple teeth formed at different times, you can get (the age range) even tighter.” Previous techniques, such as evaluating skeletal remains and tooth wear, are accurate only to within five to 10 years in adults, Buchholz said.

Here is how it works:

Carbon-14, or radiocarbon, is naturally produced by cosmic ray interactions with air and is present at low levels in the atmosphere and food. Atmospheric testing of nuclear weapons from 1955 to1963 produced a dramatic surge in the amount of radiocarbon in the atmosphere, Buchholz said.

“Even though the detonations were conducted at only a few locations, the elevated carbon-14 levels in the atmosphere rapidly equalized around the globe,” he said. Since atmospheric testing was banned in 1963, the levels have dropped substantially as the carbon-14 reacted with oxygen to form carbon dioxide, which was taken up by plants during photosynthesis and mixed with the oceans.

“Because we eat plants and animals that live off plants, the carbon-14 concentration in our bodies closely parallels that in the atmosphere at any one time,” he said.

Buchholz and his colleagues analyzed 33 teeth from 22 different people whose ages were known. The enamel separations were done at the Karolinska Institute, and sample preparation and accelerator mass spectrometry analysis was done at Lawrence Livermore.

The enamel dating technique doesn’t work for people born before 1943, because all of their teeth would have been formed before testing began in 1955.

This is pretty cool. Researchers examined several species of monkey teeth in order to determine the microwear patterns produced by a variety of different diets. They then turned their attention to the teeth of Australopithecus africanus and Paranthropus robustus:

The new study by Ungar, Brown, and colleagues suggests that, on average, A. africanus probably ate a greater share of soft and tough foods than P. robustus, which probably ate more hard and brittle foods.

The researchers found, however, that there was substantial overlap between the two species in their dental microwear, and presumably, in their diets.

Both species would probably have preferred to eat easy-to-consume, energy-rich foods, such as fruits, when they were available.

A similar phenomenon can be seen in modern chimpanzees and gorillas that live in the same geographical area. These so-called sympatric animals share food resources much of the year, but differ mostly during times of food scarcity.

At these times, gorillas fall back on tougher foods, such as leaves and stems, because their teeth and guts allow them to do so.

This study tends to confirm the idea that A. africanus and P. robustus were specializing in different diets – although not to the extent one would have thought. Seems like a good example of the competitive exclusion principle.

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"You may not be willing to admit that you resemble an ape; if your thousandth ancestor is more like an ape than you are, you may, if you wish, call it a coincidence. But if that thousandth ancestor's forebears become progressively more simian as you trace back the geneological lines, you will have to admit that somewhere in your family tree there squats an ape." Earnest Hooten

Charles Darwin

"But I had gradually come, by this time, to see that the Old Testament from its manifestly false history of the world, with the Tower of Babel, the rainbow at sign, etc., etc., and from its attributing to God the feelings of a revengeful tyrant, was no more to be trusted than the sacred books of the Hindoos, or the beliefs of any barbarian." Charles Darwin: The Autobiography